In general, a head-up display (HUD) mounted in a vehicle displays information which is necessary for driving the vehicle on a windshield glass of the vehicle. For example, the HUD displays vehicle information such as vehicle velocity, driving warnings, rear-side warnings, smart cruise control (SCC) information, lane keeping assist system (LKAS) information, and the like. Since a driver may directly check necessary driving information on the HUD while keeping his or her eyes forward (e.g., directed toward the road), the driver may minimize eye movement, thereby improving driving stability.
A conventional head-up display may implement augmented reality (AR) by outputting a nearby vehicle mark representing a nearby vehicle (e.g., a vehicle in front of, behind, to the side of, or otherwise proximate to a driver's own vehicle) sensed by the smart cruise control system, as well as an inter-vehicle distance mark representing an inter-vehicle distance between the nearby vehicle and the driver's own vehicle, so as to overlap real objects on a screen. Conventionally, when a smart cruise control function is activated and a driver then sets an inter-vehicle distance, if an actual distance between the own vehicle and the nearby vehicle is longer than the set inter-vehicle distance, there is no problem with displaying the inter-vehicle distance information on augmented reality display region of the HUD.
However, according to the related art, if the actual distance between the own vehicle and the nearby vehicle is smaller than the set inter-vehicle distance, the inter-vehicle distance information may not be displayed on the augmented reality display region. In this case, the fact that the set inter-vehicle distance is larger than the actual distance has been conventionally displayed by displaying a step within a displayable inter-vehicle distance information range on the augmented reality display region and giving a blinking effect to a trapezoidal shape which is the most distant from the own vehicle. However, it is difficult for drivers to clearly understand whether the above-mentioned blinking effect exhibits a difference between the actual inter-vehicle distance and the set inter-vehicle distance. In addition, according to the related art, if a position of the nearby vehicle moves beyond the augmented reality display region, it is difficult to display the inter-vehicle distance from the nearby vehicle, even in the case in which the inter-vehicle distance is set.